This invention generally relates to vehicle suspensions. More particularly, this invention relates to an arrangement for maintaining a desired dock height of a vehicle under selected conditions.
Vehicle suspensions are well known. Many arrangements for trucks or other heavy vehicles include air-based suspension components commonly known as air springs. Typical arrangements include a dump valve to exhaust air from the air springs when vehicle parking brakes are applied. As air is evacuated from the air springs, the height of the trailer or rear end of the truck (depending on the vehicle configuration) typically drops from a ride height until an appropriate suspension component rests on a jounce bumper internal to the air springs. It is desirable to exhaust the air from the air springs to provide a stable trailer deck for safely loading and unloading cargo from the trailer or truck.
A difficulty associated with conventional arrangements is that when the trailer or rear end of the truck drops as air is exhausted from the air springs, there is an undesirable mismatch between the trailer deck height and the loading dock height. Under some circumstances, a mismatch between the trailer deck height and the dock height prevents a forklift or other vehicle from moving into and out of the trailer for transferring the cargo.
One proposed solution has been to include a non-dump height control valve such that air is not evacuated from the air springs when parking brakes are applied This solution is not ideal, however. In many instances, attempting to load or unload a trailer without first exhausting air from the air springs results in undesirable bouncing and creates a possible safety concern. It is best to have the truck or trailer as stable as possible during loading or unloading operations.
Accordingly, there is a need for a safe and stable arrangement that allows loading and unloading a trailer while maintaining a desired height of the deck of the truck or trailer. This invention addresses that need and avoids the shortcomings and drawbacks of prior attempts.
In general terms, this invention is a vehicle suspension assembly having a dock height holding device. An assembly designed according to this invention includes a first support member attached to a body of the vehicle. A second support member moves relative to the first support member. At least one air spring is coupled with the first and second support members to provide load transfer and relative movement between them. A height holding device is positioned within the air spring and supported on one of the support members. The height holding device has a moveable portion that is moveable from a first position where the moveable portion permits relative movement between the support members (such as during normal driving conditions) into a second position where the moveable portion prevents relative movement between the support members (such as during loading or unloading).
The height holding device preferably includes a hydraulic ram that is moved into a position to maintain a desired height of a trailer deck or truck bed, for example.
The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiments. The drawings that accompany the detailed description can be briefly described as follows.